Automatic train-control system



Oct. 29,1929. N. D. PRESTON AUTOMATIC TRAIN CONTROL SYSTEM Filed Sept.10, 1924 2 Sheets-Sheet Oct. 29, 1929. N. D. PRESTON AUTOMATIC TRAINCONTROL SYSTEM 2 Sheets-Sheet 2 HIIIIP HI I I Filed Sept. 10, 1924Patented Get. 29, 1929 NEI :0. rennsron, or nocnnsrnfa, NEWYORK,'ASSIG1\TOR 'ro GENERAL RAILWAY SIGNAL COMPANY, or nocnns'rnn, NEWroan p AUTOMATIC TRAIN-CONTROL SYSTEM This invention relates toautomatic train control systems for railroads, and more particularly tosystems of the intermittent inductive type in'which continuing speedrestrictions are enforced under unsafe trafiic conditions.

In accordance with this invention, it is proposed to automatically applythe brakes and stop the train, unless the engineer takes an appropriateaction, conveniently termed acknowledgement, at each caution signal orcorresponding control point, and also at each stop or'danger signal. Itis considered that the enforcement of such acknowledgement on the partof the engineer will serve to stimulate and maintain his vigilance,thereby assuring greater safety of train movement, inasmuch as failureof both the train control system and the engineer must occur before anaccident can result. According to this invention, such acknowledgementis required at each successive stop signal.

' According to this invention, the engineer- 7 is obliged to reduce thespeed of his train, if

necessary, after passing each caution signal, so as to be prepared tostop at the'next signal or block entrance, otherwise an automaticapplication of the brakes occurs; and this requisite is satisfied in asimple and direct manner 39 by requiring the engineer to initiate abrake application or have the brakesacting, if the speed is above someselected minimum speed.

Various other characteristic features, advantages, and specific objectsof this inven tion will appear hereinafter as'the descriptionprogresses. f 1

In describing the invention in detail, reference will be made to theaccompanying drawings, in which Fig. 1 shows in a simplif 40 fied anddiagrammatic manner the trackway equipment and locomotive equipmentconstituting one embodiment of the invention and adaptable for trainmovement on double track railroads, the parts and circuits being shownmore with the purpose of facilitating explanation and understanding ofthe nature and character of the invention than with the ideaofillustrating the'construction and arrangement of parts that wouldprobably be employedinpractice; and Fig. shows dia- .phore signals "7are shown conventionally,

grammatically and in accordance with'estab lished invention the trackwayequipment for an intermediate signal location on a single track railroadequipped with an automatic block signal system of the type commonlyknown as the absolute-permissive-block sys- Referring to Fig. 1 of theaccompanying drawings, the track rails 1 are divided into track sectionsor blocks by insulated joints 6] 2 in the usual way, one complete blockE, with the adjacent ends of two other blocks D and F being shown. It isassumed forthe purposes of explanation that each blockwill be at leastas long as braking distance forthe normal running speed on the railroad,and will include only one track circuit. The parts and circuitsassociated with each of. these blocks will ordinarily be the same; butfor simplicity in illustration there, is shown in Fig. 1 only theequipment for the-block E. Each block is provided with the well knownnormally closed track circuit, including a track relay 3 and a trackbattery 4:. As shown, a relay 5 is included in. series with the trackbattery 4;, this relay being of suitablecone struction and serving itswell known purpose of attracting its armature and closinga normally openfront contact 6 upon the entrance of a train into the'correspondingblock.

This system oftrain control is preferably used in conjunction withtrackway block signals. The particular type of block signal and its-formof control circuits may be any one of the kinds well known'inthe art;Semawithout attempting to illustrate any particu; lar form of controlcircuits, it being assumed that these signals will be ofthe usual threeposition type and controlled accordingly.

The controllmg lnfluences or impulses {for the automatic train controlsystemare com;

'municatedor transmitted according to this. 7

invention by magnetic induction between trackway devices and receivers,the action taking place through an intervening air gap and withoutphysical contact. These control ling impulses are transmitted onlyatprede termined points along the trackway where the track devices arelocated, and the system of this invention is accordingly of theintermittent inductive type.

The track device for bringing about automatic control, convenientlytermed the initiating track device, is designated a whole T andcomprises a permanent magnet 8, made up of a suitable number of sectionsof a general U-shape, in this instance shown disosed horizontallybetween the track rails 1.

ecured to the ends of this permanent mag-- net are vertically disposedsoft iron cores 9, which have lateral extensions 10 projected towardeach other and affording a leakage path for the magnetic fiux of saidpermanent magnet, said leakage path being of relatively higherreluctance than the flux path through the receiver later to bedescribed. The cores 7 V netic field above the track device; whereaswith these coils on open circuit and deenergized, said permanent magnetproduces an active magnetic field above the track device thru which thereceiver on the passing locomotive or other vehicle must pass.

- The initiating track devices T may be located at different points inthe several blocks as desired; but the preferred arrangement consists inlocating one such track device in each block at braking distance for theselected minimum speed in the rear of the insulated 'oints defining theexit end of that block. uch a track device T is shown in the block E.-In the case of long blocks, or under other circumstances as desired, inaddition to the initiating track device near the exit end of each block,as just described, there may also be another initiating track device inthat block at braking distance from the exit end thereof for the normalrunning s eed of trains. Such a track device T is s own in the block E.Theinitiating track device near the exit end thereof is employed to stopa train short of the end of the block, if the next signal in advance isin the danger position, unless the engineer takes appro- 'priate action.In other words, this track device, such as T is employed to enforceacknowledgement of each stop signal. The same track device may be used,if desired, to enforce acknowledgement of a caution signal and controlthe car equipment so as to compel a reduction in speed in obedience tothe caution signal; or a separate initiating track device, such as T,may be employed in each block as the cautionary device.

Associated with each block is a reset or restoring track device, whichis located near the exit end of each block. This reset track device TRcomprises a soft iron core, preferably in the form of the generalU-shape and provided with enlarged pole pieces. On the legs or back yokeof this core is wound a coil 12, and when this coil is energized, amagnetic field exists above the reset track device. For reasons whichwill appear hereinafter, in the particular form of the invention shown,the reset track device is located outside of one of the track rails andis disgoverned in various ways, by line relays,

track relays, or circuit controllers on the associated block signals. Inorder to economize in battery consumption, arrangements are shown suchthat the coils 11 and 12 of these track devices are normally deenergizedand are automatically energized upon-the approach of the train.

The energizing circuit for the reset track device TR may be traced asfollows :-co1nmencing at the coil 12, wire 13, armature 6 of relay 5 andits front contact, wire 14, front contact 15 of the track relay 3 of theblock next in advance, wire 16, battery 17 and wire 18.

The energizing circuit for the neutralizing coils 11 of the cautiontrack device T may be readily traced on the drawings and includes abattery 19 and the front contact 20 of a relay 21. The energizingcircuit for the relay 21 includes a back contact 22 of the track relay 3of block in which said track device is located and a front contact 23 ofthe track relay 3 of the next block in advance.

The other or stop signal initiating track device -T has an energizingcircuit forits neutralizing coils 11 which may be traced as follows:commencing at coil 11, wire 24, front contact 6 of relay 5, wire25,.front contact 26 of track relay of block next in advance, wire 27,battery'28, and wire 29 back to the coils 11.

The locomotive or other railroad vehicle is shown diagrammatically astwo pairs of wheels and axles 30. Operated by one of these axles is anautomatic reversing switch X, which in the simplified form showncomprises a pivoted switch arm 31coupled by a link 32 to the outer endof a swinging arm 33 mounted to turn freely on the axle 30. A frictionshoe 34 is carried by said arm 33 and is pressed against the axle 30, ora collar thereon, by a compression spring 35, thereby forming africtional connection between the arm 33 and the axle. In Fig. 1 thenormal direction of traffic is from left to right as CD I indicated bythe'arrow; and assuming a train movement in this direction, it will beevident that the arm 33 is moved by friction,as the axle turns, to theupper position shown. If the locomotive should back up, or should run inthe, normal direction of trailic with the other-end ahead, the reversingswitch X wouldbe operated to the other position, shiftin the switch arm31 to its lower position.

. buitably supported on the locomotive is a receiver-R disposed inposition to cooperate with the initiating track devices T and T Thereceiver R, in the simplified construction shown, comprises two enlargedpole pieces or collector plates 36, with extensions separated by anair-gap; and a pivoted armature 37 spans this air-gap, said armaturebeing held in a retracted position by a suitable spring 38. Thisarmature 37 carries a suitahis contact arranged to engage an insulatedstationary contact, shown conventionally as an arrow, when said armatureis in its retracted position. It will be evident that, when the receiverR passes thru the magnetic field of an active track magnet T or T themagnetic field of this track magnet will be collected by the pole pieces36 and concentrated across the air-gap of the armature 37, therebyattracting this armature in opposition to the spring 38 and opening itscontacts.

In the particular form of the invention shown two receivers RR areemployed, one on each side of the locomotive in position to pass overthe reset track device or magnet TR. These reset receivers RR areconstructed alike, substantially the same as the receiver R, having anormally spring retracted armature 39. The contacts of the armature 39of the reset receivers, however, are normally open and are closed by theattract-ion of this armature.

The locomotive or car equipment includes a plurality of relays P, S andQ of suitable construction, which are preferably quick acting, protectedby spring supports against operation by vibration, and otherwiseconstructed in accordance with recognized practice so ast-o be adaptedfor their respective duties. The car equipment also includes a suitablespeed responsive device or governor G, connected to and driven from thecar wheels and acting to open contacts 40 whenever the speed of the caris above-some selected minimum speed, such as fifteen or twenty milesper hour. This speed responsive device G may be of any suitableconstruction and is shown in'a simplified manner as being of the wellknown centrifugal type.

It isassumed that the automatic application of the brakes will beproduced by a suitable application valve or equivalent means, presumablycontrolled by an electro-pneumaticvalve. The particular type of brakeapplying means is not material to the present invention and has not beenillustrated. A

conventional form of electro-pneumatic'valve I EPV has been shown toillustrate the manner 'of control for the brake applying means.

It is assumed that this system of train control will be applied to alocomotive or other railway vehicle equipped with the usualairbrakesystem', including an engineers brake a simplified and diagrammaticmanner and comprises two diaphragms 42 and 43 closing the ends ofenclosed chambers 44 and 45. In the chamber 44 and actingagainst thediaphragm-42 is aspring 46 having a strength corresponding to about 20pounds per square inch on the diaphragm 43, a 20 pound reduction beingassumed as constituting the desired brake application. The diaphragms 42and 43 are connected by member 47 which, by

the action of an insulated projection or equivalent means, acts to closecontacts 48 when these-diaphragms are shifted; to the left in oppositionto the spring 46. The chamber 44 is in communication with the regularequalizing reservoir of the air brake system;

whereas the chamber45 is in communication with the lowpressure side ofthe feed valve, so that the pressure in this chamber 45 cor respondswith the normal running brake pipe pressure. t ermined reduction intheequalizing reservoir pressure, assumed to be 20 pounds in this instance,the pressure in the chamber 45 overcomes the reduced pressure in chamber44 lus that of the spring 46, and shifts the diaphragms and theirconnecting member 47 to the left, thereby closing the contacts 48. Theengineer may make the reduction in one or more stages. The contacts 48do not close until a reduction has been made in'equalizing After theengineer makes a predereservoir pressure which in time will bring out abrake application of th d i d f; fectiveness. v i

The act of acknowledgement hereinbefore mentioned has been taken toconsist in manual operation of a suitable push. button or contactor.This acknowledging contactor AC is located at a convenient point inthecab and readily accessible to the engineer; In;

the form shown, this acknowledging con- .tactor comprises a plunger 49and two contacts or switch arms 50 and51. The plunger 49 is urged toitsupper position by a spring 52. When this plunger is depressed by theengineer in opposition to the spring 52, the

contact arm 50 is moved at lonceinto engagement with astationary'contact, shownas an I equipment in the normal position shown,with arrow. The other contact arm 51 is released by such downwardmovement of the plunger 49, but its downward movement, brought about byan auxiliary springv53, is retarded by a suitable dash-pot device 54, sothat the resilient finger 55 of said contact arm 51 is not moved farenough to be disengaged from its cooperating contact (shown as an arrow)until after the plunger 49 has been held in the depressed position for ashort interval of time, such as five or six seconds. The arm 51 returnsquickly to its upper position.

In case the engineer fails to take appropriate action at each cautionsignal, or corresponding control point, or at each stop signal, it isdesired to inflict some form of penalty'in order that the engineer maybe obliged to remain alert. Such penalty'may take various forms, but inthe arrangement shown, the train must be brought to a stop and theapparatus restored by operation of a reset switch BS which is accessibleonly from the ground. The reset switch RS comprises a push button orplunger 56 with normally closed contacts 57 and normally open contacts58.

Opemzfion.The parts and circuits of the car equipment are shown in Fig.1 in the normal position. The circuits have been shown. in simplifiedmanner, embodying the symbols B and C to indicate the terminals of a carbattery, turbo-generator, or other suitable source of current; and thecircuits will be traced from B to C. The primary relay P is maintainedenergized by a stick circuit as follows :-commencing at B, front contact60 of relay P, wires 61 and 62, relay P, wire 63, armature 37, and itscontact to C.

The relay S is maintained energized by a stick circuit which may betraced as follows ;commencing at B, front contact 64 of relay S, wires65 and 66, relay S, wire 67 and front contact 68 of relay P to C.

' The relay Q is energized by a stick circuit which may be traced asfollows :-commencing at B, front contact 69 of relay P, wires 7 Oand 71,timed contacts 5551of acknowledging contactor AC, wires 72, 7 3, frontcon tact 74 of relay S, wires 75, 76, relay Q, wires 77 and 78, andfront contact 79 of relay Q to C.

With the relay Q energized, theelectropneumatic valve EPV is maintainedenr gizcd by circuit commencing through front Contact 80 of relay Q,wire 81, valve EPV, wire 8:2 and normally closed contacts 57 of thereset switch RS to C.

Entering caution block.-Assimiing the car the relays P, S and Q.energized as just oescribed, suppose that the car passe into a cautionblock, that is, a block next in the rear of an occupied block. Forinstance, assume a train 1n the block F, making the block E a cautionblock. As the following car or train enters the block E, the track relay3 is shunted and closes its back contact 22, but the relay 21 cannot beenergized, because the front contact 23 of the track relay 3 of theblock F is open. Consequently, the deflecting or neutralizing coils 11of the track magnet T are on open circuit, and an active magnetic fieldexists over this track magnet. -As the receiver R passes through thismagnetic field, its armature S7 is attracted, interrupting the stickcircuit for the relay and causing its armature to be retracted and openits front contacts. The opening of the front contact 68 of the relay Pbreaks the stick circuit for the relay S, which is thereby deenergizedand remains deenergized until restored by passing an active resetmagnet. Upon deenergization of the relay S, the closure of its backcontact 64 together with wire 83, establishes a connection to B inmultiple with that through the front contact 60 of the relay P; andsince the opening of the contacts of the armature 37 of the receiver Ris only momentary, the relay is (prickly reenergized.

The opening of front contact 69 of the relay although only temporary,interrupts the k circuit for the relay Q, heretofore traced would causedeenergization of this relay, as at tne time of the opening of saidfront co react 69, the engineer has the plunger 49 of hisacknowledgingcont actor depressed so asto close the contacts 50 andestablish a connection to B throi these contacts and wire 84, in c withthe connection to B through contact 69. In other words, unless ..eertakes the appropriate action by manuari operating the acknowledgingconmanipulation, the contacts 55 open after a .ime and interrupt thecircuit for the relay Q, thereby applying the brakes. In short, theengineer must restore the acknowledging contactor AC to normal aftereach manipulation, otherwise the brakes are applied. The time intervalprovided for thecontacts 51 is selected so as to afford the engineerreason able latitude in the manipulation of this cont actor, but isshort enough to prevent the engineer from acknowledging by one act twosuccessive signals or control points.

Unless the speed of the train at the'time the relay S is deenergized isbelow the'minimum speed, so that the contacts 40 are closed and togetherwith wires and 86 establish a shunt around the front contact-74L of therelay S, the engineer must either have his brake valve in the serviceposition, or must have made the required reduction in equalizingreservoir pressure, otherwise the stick circuit for the relay Qis'interrupted, the brakes are applied and the reset switch RS must beoperated from the, ground before the train can proceed. If the engineerhas his brake valve in the service position, a multiple path or shuntaround the front contact 74 of the relay S is established by wire 87,con tacts 41, and wire 88; and similarly, if a pre determined reductionhas been made in the equalizing reservoir pressure, closing cont-acts48, a like multiple path or shunt is established through wire 89contacts 48 and wire 90.

By reason ofthe construction and arrangement just described, theengineer iscompolled to reduce the speed of his train, unless below theminimum speed, after passing the caution track magnet, with the resultthat the train is safely controlled. It will be observed that if theengineer should move his brake valve outof'the service position beforemaking sutficient reduction in equalizing reservoir pressure toclose'contacts 4,8, or should attemptto release the brakes after closureof these contacts, which would im-. mediately open upon movement oftheengineers brake valve to the release 'or running positions, the relayQ, would be deenergized, since the front contact 741 01? the relay Sremains open thruout the caution-block.

Ac/mmliedgment at a stop signaZ.'For reasons already explained, it isconsidered important to require the engineer to acknowledge each stopsignal. This is done by automatically applying the brakes unless theengineer takes appropriate action. Since such acknowledgement isrequired to assure safe control of the train in case the engineer isincapacitated,- it is considered essential that the point where suchacknowledgment is required should be so located that, if noacknowledgment is made and an automatic brake application occurs, thetrain will be stopped short of the point of danger. For this reason, thetrack device or magnet T is located braking distance for the minimumspeed from the exitend oftheblock.

As the locomotive or car passes the track magnet T, which is in thedanger condition with the block F occupied, due to the opening of thefront contact 26 of thetrack relay 8 the armature 37 of the receiver Ris attracted again and the relay P is again mo.- mentarily deenergized,such "deenergization occurring even though the relay S is deenergized,because the armature 37 breaks the connection to C through the relay P.If at the time of such momentary deenergization ofthe relay P, and theaccompanying opening of its front contact 69, the engineer does not havethe'plunger of the acknowledging contactor AC depressed, the quickacting relay Qis deenergized and the brakes applied. T his automaticbrake application occurs even thoughthc running speed is below the lowspeed limit, and the contacts 40 are closed.

The relay Q, is, of course, made quick acting .so as to open in theinterval of time that the armature 37 of the receiver is in theretracted position, it being noted that this time is longer because thespeed of the train is low. The same acknowledgment 1s required at eachsuccessive stop signal, since the relay P 1s deenergized at eachactlvetrack magnet,

Also, if two track magnets are used in a comotive is traveling inthenormal direction of traflic. It will be observed that the coil 12 ofthe reset track magnet TB is energized if the next block in advance isnot occupied.

Assume that a train has passed thru a cau tion block and that in themeantime the block in advance has cleared up. As thetrain approaches-theentrance to the unoccupied block and passes over the reset trackmagnetTR which is energized under these conditions,

35 track device requ res ac the armature 39 of the correspondingresetreceiver is attracted, establishing api'ck-up circuit for the relay S,as follows :-commencing at B, armature 39, wire 91 or 92, as the casemay be, reset switch 31, wires 93 and 66, relay S, wire 67 and frontcontact 68 of relayP to C. Upon reenergization of the relay S the normalstick circuit for the relay Qis reestablished, and the train may proceedat its normal runningspeed without interference. In this connection itwill be obvious that, if desired, speed contacts, opening aboveaselected maximum speed, maybe inserted in series with the front contact74k of the relay S, thereby providing a maximum speed limit. As shown,there is no maximum speed limit enforced under clear traflic conditions.

In case the engineer fails tov acknowledge an active initiatingtrackmagnet, or fails to make timely initiating of a manual brake applicationwhileexceeding thelow speed limit for other than clear trafficconditions, and the relay Q; becomes deenergized, it is necessary forthe engineer to operate the refore, protect the reset switch RS againstcountered in practice.

abuse and prevent it from being carelessly or maliciously left in theoperated position. Briefly summarizing the operation of the system ofthis invention, it will be observed that acknowledgement is required foreach caution signal and for each stop signal, or corresponding controlpoint. In the preferred. arrangement of track devices, such as shown inthe block E, the acknowledgment of the caution signal takes place at thedevice T in advance of the signal and at least braking distance for thenormal running speed from the exit end of the block; and theacknowledgement of the stop signal occurs at the device T locatedbraking distance for the minimum speed from the exit end of the block.This arrangement requires two initiating track devices for each block,but is consideredto be the preferable arrangement for'the conditionsordinarily en- In the interests of safety, as herein before pointed out,the track device T forcing acknowledgement for the stop signal, shouldbe located in the rear of the signal, and must be effective if thesignal is at stop, though not necessarily if the signal is at caution.This same track device T could be used as the cautionary track device,but such an arrangement would have the objection that acknowledgementwould be required at a distance in the rear of a caution signal and ata'point where the signal might not be readily visible, and also that aspeed reduction would be compelled before reaching the caution signal.Regarding the reset magnet, in View of the foregoing explanation ofoperation it can be seen that this magnet should be located close to theexit end of each block, so that a train will not receive a resettingimpulse if there are any cars between the reset magnet and the end ofthe block. Also, the reset magnet should be in the rear of thecautionary initiating track device, assuming that the reset magnet willbe used to clear up the car apparatus at a caution signal as well as ata clear signal, otherwise the initiating impulse received at thecautionary track mag- Ilet might be improperly nullified by the resettrack magnet. So long as the fundamental principles mentioned and otherretrack magnet being of course located and' controlled accordingly.

Single track 0perat2'oa.-On single track railroads, trains normally movepast signals and conrol pointsin both directions, and

since the train control system must be capable of safely regulatlng trammovement in either direction, special problems are presented in applyingtrain control systems to single track railroads. Fig. 2 shows onearrangement of track devices and control circuits applied to anintermediate signal location of a single track block signalling sys temof the Well known type commonly termed an A. P. B. system. The circuitarrangements and devices constituting an A. P. B. system are nowgenerally known and recognized in the art, so that detail illus-'tration and description is unnecessary. One specific form of an A. P. B.system is shown and described in detail in the patent to Wight No.1,294,736, dated February 18, 1919, to which reference may be made for adisclosure of the specific means utilized to obtain the operations andresults herein generally explained.

Referring to Fig. 2, the adjacent ends of two blocks K and'L areillustrated, these blocks being provided with track relays 98 and 99,respectively. The signal 100, which is of the usual three-position type,governs traffic from left to right, from the block K into the block L;and a similar signal 101 governs traffic in the opposite direction fromthe block L into the block K. In the A. P. B.

its

system, when a train enters a stretch of single track, all of theopposing signals governing trafiic in theopposite position assume thedanger or stop position. A train approaching from the left in Fig. 2 andpassing from the block K into the block L will, therefore, find thesignal 101 at stop, irrespective of the presence of other trains. Thesignals, such as in the case just assumed, governing traffic in thedirection in which the train is running are automatically controlled tothe clear, caution, or danger position by the presence of other trainsahead in the same way as on a double track. Associated with each of thesignals in an A. P. B. system is a directional stick relay which isnormally deenergized and which is automatically energized upon passageof a train by the corresponding signal in the direction of traflicgoverned thereby. Referring to the signal 100, the stick relay ST 100 isenergized when a train, traveling from left to right, passes the signal100, and this relay is maintained energized until the rear end of thistrainhas advanced beyond the next signal ahead governing traffic in thesame direction. The other stick relay ST 101 for the signal 101 iscontrolled in the same way. The particular circuits and devices for thuscontrolling these stick relays ST 100 and ST 101 are not material to thepresent invention and have not been illustrated, one arrangement of suchcontrol circuits and devices being shown and described in the patent toWight above mentioned. ,F or simplicity in illustration and explanation,the controls for the track devices have been shown in Fig. 2 asaccomplished by the opening and closing of circuit controllers operatedin the usual way in accordance with the position of the signal. Thesecircuit controllersare shown in accordance with established convention.There are three circuit controllers for each signal, those for thesignal 100 being designated 102, 103 and 104, the corresponding circuitcontrollers for the other signal 101 being given the same refer- 'encenumbers with an exponent. Circuit controller 102 is closed only if thesignal is inits 90or clear position. Circuit control ler 103 isclosed'with thesignal in the 90 or clear position, or in the 45 orcaution position, or'any intermediate position between these two. Thecircuit controller 104 is closed from 90 to 45, the same as the circuitcontroller 103. 7 i

' The cautionary initiating track device T is located at the signalssubstantially opposite the insulated joints defining the block ends.This track device is disposed midway between the track rails andinfluences a re-;

ceiver R on a car passingthereby in either dlrection. There are two.energizing circuits for theneutralizing coils 11 of the.

track magnet T, these circuits beingsimilar, so that the tracing of onewill make both clear. One of these energizing circuits, controlled bythe signal 100 may be traced as follows: commencing at lower coil 11,wire 105, battery 106, wires 107 and108, back contact 109 of track relay98 of block K, wire 110, circuit controller 102, wires 111 and 112'backto the other coil 11.

7 Assuming a train approaching from the left, the opposing signal 101will be at stop. hen the approaching train enters the track section K,the track relay 98 drops and closes its back contact 109; and if thesignal 100 is then in the clear position, the neutralizing coils 11 ofthe track device T are energized and said track device is renderedinactive. If the signal 100 is in the caution or stop position, thecircuit controller'102 interrupts the energizing circuit for the coils11, render- 'ing the track device T active. The same eX- planationapplies for train operation in the other direction, the circuitcontroller 102 of the coils 11 in this instance.

The initiating track device enforcing acknowledgement of a stop signal,as previouslyexplained, is located braking distance for the minimumspeed in the rear of the corresponding signal. The track device T forthe signal 100 has two energizing cir cuits for its neutralizing coils11, one through the back contact 113 of the track relay 98 and throughthe circuit controller 104 of the signal 100, the other circuitincluding a front contact 114 ofthe opposing stick relay ST 101.Assuming a train traveling from left to right, the stick relay ST 101 isdeenergized; and when this train enters the track section K and dropsthe track relay 98, closing its back contact 113, the coils 11 of thetrack device T are energized, providing the signal 100 is in either theclear or caution position. 7 If the signal 100 is in the stop position,the coils 11 of the track device T; are on open circuit, and theengineer must acknowledge. The stick relay ST 101 picks up for a traintraveling in the other direction, from right to left, closing its frontcontact 114 to'energize the coils 11 of the track device T irrespectiveof the position of the signallOO. Consequently, the track device'T forthe. signal 100 is always inactive fora train traveling in the oppositedirection, due to the control of the stick relay ST 101. .The sameexplanation applies to the control of the track device T for signal 101.

The reset magnets for both directions are controlled in the same way ason double track, except that a back contact 115 of the adjacentt'rackrelay isused instead of the front contact of a relay in series with thetrack battery, and a circuit controller on the signal instead of a frontcontact of the track relay next in advance, For-example,

the energizing circuit for the reset magnet TR fortraflic' moving fromleft to right'in" the direction governed by the signal may be traced asfollows :-starting at the reset magnet TR, wire 24, back contact of thetrack relay 98 of the block K, wire 25,

circuit controller 103 of the signal 100., wire 27, battery 28 and wire29 back to the'reset magnet. The automatic reversing switch X rendersthe proper receiver on the locomotive effective "to cooperate with thecorrect reset track device.

' The invention has been disclosed in a simple term, divested of manyfeatures of constructi-on' and operation that might be desirable inpractice and it should be understood that various eXpedients may beemployed in connection with the specific means of cab si -nals andautomatic control with the giving of a distinctive signal, While inunequipped territory, and the like. Moreover, the invention is notrestricted to the particular construction, combination or arrangementsof parts and circuits herein disclosed, but is susceptible of widevariation in the particular form of means employed. Various chan es,adaptations, additions, and modifications may be made in the particularembodiment of the invention disclosed, without departing from theinvention or deviating from the fundamental concept of means underlyingthe invention.

What I claim is 1. In an automatic train control system, the combinationwith a traffic controlled track device providing a local ma netic fieldwhen in the active stoppin condition, an armature on a car attracted bythe magnetic field of said active track device, means on the carcontrolled by said armature and tending to cause an automaticapplication of brakes on the car, and manually operable means eii ectiveonly ii actuated prior to the attraction of said armature for preventingsuch application of the brakes.

2. In an automatic train control system, the combination with a trackmagnet producing an external local magnetic field when in the activestopping condition, of automatic brake control apparatus on a vehicle,control means on the vehicle, operated by magnetic attraction whilepassing through the magnetic field 01" said trackmagnet and tending tocause operation of said apparatus, and manually operable means on thevehicle effective for a limited time only after each manual operationand capable of preventing operation of said apparatus only it manuallyoperated prior to the operation of said control means.

3. In an automatic train control system, means on a vehicle including anelectro-magnetic valve and acting upon the regular air brake equipmentofthe vehicle to produce an automatic brake application uponde-energization of said valve, a stick relay on the vehicle controllingsaid valve and having a stick circuit including contacts of the relayclosed only it said relay is energized, a traitfic controlled trackmagnet producing a local magnetic field under dangerous trafiic conditions, an armature on the vehicle attracted by the magnetic field ofsaid track magnet and when attracted interrupting said stick circuit,and manually operable means for main taining said stick relay energizedindependently of the break in its stick circuit made by the action ofsaid armature, said manually operable means having a limited time ofeffective action and being effective only if actuated prior to theattraction of said armature.

4. An automatic train control system for railroads comprising, a trackdevice producing'a local] magnetic field when in its active stoppingconditon, brake control apparatus on a vehicle, impulse receiving meanson the vehicle including relay temporarily de-energized by the influenceof the magnetic field of said track device, said relay when thusdeenergized tending to cause operation of said brake control apparatus,and manually controllable means including a stick relay for preventingsuch operation of said brake control apparatus, said manuallycontrollable means being effective only if actuated prior to operationof said apparatus and only for a limited time after each manualoperation.

5. In an automatic train control system, the combination with a brakecontrol device ef fective when active to automatically apply the brakesof a vehicle and maintain such brake application until the vehicle hasbeen brought to a stop, of intermittent inductive impulse transmittingmeans acting at predetermined control points along the track to produceinitiating and restoring influences on the vehicle in accordance withthe presence or absence of other trains ahead, speed con rol apparatusincluding a speed responsive device driven from the wheels of thevehicle and rendered effective by said initiating influences to actuatesaid brake control device if the running speed of the vehicle thereafterany time exceeds a predetermined low speed limit, said speed controlapparatus being restored to normal by said restoring influences, controlmeans temporarily influenced by said initiating influences for tendingto actuate said brake control device, manually operable means effectivefor a limited time for each operation and only it operated prior to theactuation of said brake control device for maintaining it inactive inspite of its control by said control means, and other manuallycontrollable means for maintaining said brake control device inactive inspite of said speed control apparatus only so long as the engineer isinitiating a manual brake application or is maintainng a completed brakeapplication.

6. In an automatic train control system for railroads having tracksdivided into blocks, a track magnet near the exit end of each block atbraking distance for a predetermined low speed from the eXit end of saidblock, each track magnet comprising a permanent magnet and neutralizingcoils and producing a local magnetic field it the next block in advanceis occupied, brake control apparatus on the vehicle tending to producean automatic brake application at the time of movement of the vehiclepast an active track magnet, and manually operable means effective onlyif actuated prior to the operation of said apparatus for preventing suchbrake application, said manually operable means being eilective for alimited time only after each manual operation thereof.

7 thereof, impulse receiving means on the ve 7. In an automatic traincontrol system for I railroadshaving tracks divided into blocks, a trackdevice associated with each block and assuming an active stoppingcondition if the next block in advance is occupied, brake controlapparatus on a vehicle including a speed responsive device driven fromthe wheels apply the brakes automatically whenever the" speed of thevehicle exceeds a predetermined low speed limit, sa1d apparatusincluding a stick relay which if ale-energized produces a,

brake application that cannot bereleased until the vehicle has beenbrought to a stop, a normally open energizing circuit for said stickrelay, and manually operable means for closing said circuit for alimited time only, said manually operable means being effective only ifactuated prior to the reception of an impulse by said impulse receivingmeans.

8. Car apparatus for train control systems comprising, brake controlapparatus including an electro-pneumatic valve for automaticallyapplying the brakes on de-energization of said valve, a normallyenergized stick relay maintaining said valve energized, a stick circuitfor said relay, separate circuit controlling devices for interruptingsaid stick circuit, one of sa1d circuit controlllng devices beingtemporarily opened in response to control influences from the trackway,the other of said circuit control devices being maintained open so longas dangerous tralfic conditions exist, manually operable means forestablishing a shunt around the first circuit controlling device for alimited time, and other manually operable means for maintaining a shuntaround the other of said circuit controlling devices only so long as theengineer is initiating or maintaining a manual brake application.

9. In a train control system for single track railroads, equipped withan absolute-permissive-block system ofthe character described, thecombination with a signal governing traliic in one direction, of a trackdevice opposite said signal and located symmetrically on the center lineof the track, a control circuit for said track device acting when closedto render it inactive, means operated in accordance with the directionand movement of trains by said signal for opening sa1d control circuitwhen a train approaches sa1d signal in the direction of traffic governedthereby and there is another train in advance, a reset track elementlocated on one side ofthe center line of the track and in the rear ofsaid signal, and means for rendering said second track element activeirrespective of the direction of train movement it the track in advanceof said signal and protected thereby is unoccupied. v

absolute-permissive-block signal system, the

combination with an intermediate signal, of

a track element for governing traflic in both directions, and a resettrack elementcapable of cooperating with trains moving in the directionof trafiic governed by said signal only, and automatic means forgoverning and controlling the condition of track elements in, accordancewith trafiic conditions.

11. A train control system for single track railroads comprising, incombination with the intermediate signals of anabsolute-permissive-block "system, of a reset traclr magnet for eachsignal located one side of the center and automatic means operated tronithe run-,

ning gear of the vehicle for connecting said train control apparatus tothe receiving device on that side or" the vehicle on which are locatedthe reset magnets associated with the signals that govern traflic inthedirection the v vehicle is then running.

12. In a train control for single track railroads equipped with anabsolute-permissiveblock signal system, thecombinatio-n with theintermediate signals of said block signalsystem, of a reset trackelement for each signal, active it the portion of track in advancethereof and protected thereby is vunoccupied, initiating track elementsadjacent said signals, means responsive to the direction of the trainmovement for governing the controlling condition of each initiatingtrack element in accordance with the presence or absence of trains inadvance of the associated signal when a train approaches said signal inthe direction of traflic governed thereby, a vehicle equipped with brakecontrol apparatus having its operation dependent upon the running speedof the train, a receiver carried by said vehicle inposition to cooperatewith the initiating track element irrespective of the direction in whichsaid vehicle moves set receivers, to the brake control apparatus ofbraking distance for a predetermined low speed from said exit end, brakecontrol apparatus on a vehicle including a speed responsive devicedriven from the wheels thereof and acting when rendered active toautomatically apply the brakes if the running speed of the vehicle atany time exceeds said predetermined low speed, an impulse receiver onthe car cooperating with said t-rackway impulse device for renderingsaid apparatus active, means governed by said impulse re ceiverintending to automatically apply the brakes independently of speed for alimited time at each active trackway impulse device, a manually operableacknowledging device on the vehicle effective for a limited time andonly if operated prior to the reception of said impulses for preventingthe brake application by said means, and means for automaticallyrestorin said apparatus to normal and remove the low speed limit at theentrance to each unoccupied block. i

g 14. A train control system of the intermittent inductive typecomprising, trackway and car-carried apparatus cooperating to apply thebrakes irrespective of the speed of the car at a predetermined controlpoint at braking distance for a loW speed limit in the rear of each stopsignal, a manually operable acknowledging device effective to forestallsuch brake application, provided it is operated prior to such brakeapplication, said acknowledging device being effective for a limitedinterval only when maintained in its operated condition, and brakecontrol means including a speed-responsive device driven from the wheelsof the car and governed by said trackway and car-carried apparatus toestablish a restricted speed limit which the car cannot exceed withoutan automatic application of the brakes, said manually operable devicebeing inefiective to prevent such brake application due to excessivespeed.

15. A controlling element for train control systems comprising a circuitcontroller, and means for operating said circuit controller includingtwo diaphragms, one of said diaphragms being exposed to the action of aspring and the pressure in the equalizing reservoir of the usual airbrake system, and the other diaphragm being exposed to a feed valvepressure corresponding to the normal running brake pipe pressure.

16. In an automatic train control system for railroads having trackdivided into blocks, a track magnet near the exit end of each blockbraking distance for a predetermined low speed from the exit end of saidblock, each track magnet producing a local magnetic field if the nextblock in advance is occupied, a normally'energized relay on the vehicletemporarily tie-energized by the influence of the magnetic field of atrack magnet in its active condition, brake control apparatus upon thevehicle, said relay upon de-energization thereof tending to actuate saidapparatus, said apparatus when once actuated to apply the brakes beingmaintined in that condition and preventing release of the brakes untilrestored, means for restoring said apparatus after the vehicle has beenbrought to a stop, and manually operable means effective only ifactuated prior to the operation of said apparatus for preventing suchbrake application, said manually operable means being effective for alimited time only after each manual operation thereof.

17. In an automatic train control system for railroads having tracksdivided into blocks, an impulse transmitting device on the track nearthe entrance end of each block, a second impulse transmitting devicenear the exit end of each block at braking distance for a low speed fromsaid exit end, a control circuit for rendering each of said trackwaydevices ineffective and closed only if the block in advance of the blockin which said device is located is then unoccupied, receiv ing means onthe car including a relay temporarily de-energized by the influence ofsaid trackway device in its active condition, brake control apparatus onthe car, said relay when de-energized tending to cause operation of saidapparatus and apply the brakes, manually operable means efi'ective for alimited time only after each operation thereof and also only if operatedprior to the actuation of said apparatus by said relay, for preventingsuch operation of said apparatus, another relay on the carde-energizedby said first men tioned relay, and maintained de-energized untilrestored, mechanism on the car including a speed-responsive devicedriven from the wheels thereof and rendered effective uponde-energization of said another relay for tending to cause operation ofsaid brake control apparatus if the car exceeds said low speed, andimpulse transmitting means partly on the car and partly along the trackeffective near the exit end of each block for restoring said anotherrelay to its normal energized condition provided the next block inadvance is then unoccupied.

18. In an automatic train control system for railroads having tracksdivided into blocks, a tripping impulse device on the track near theentrance to each block and automatically controlled to assume its activestopping condition if that block or the next block in advance is thenoccupied, a reset impulse device near the exit end of each block andautomatically controlled to assume its active condition only if the nextblock in advance is not occupied, impulse receiving means on a vehicleincluding a relay momentarily deenergized by said tripping impulsedevice in its active stopping condition, a second relay on the vehiclealso de-energized by said tripping impulse device in its active stoppingcondition, said second relay when de-energized remaining in thatcondition until restored by an active reset impulse device on the track,brake control apparatus on the vehicle governed jointly by said relaysand including a speed-responsive device driven from the wheels of thevehicle, said apparatus acting while said second relay is de-energizedto permit movement of the vehicle Without an automatic brake applicationonly at speeds less than a predetermined low speed limit, said firstmentioned relay when ole-energized tending to actuate said apparatusindependent of the running speed of the vehicle, and manually operablemeans on the vehicle effective only for a limited time after eachoperation and only if actuated prior to the operation of said brakecontrol apparatus for temporarily preventing operation of said apparatusby de-energization of the first relay, said manually operable meansbeing inefiective to prevent operation of said apparatus uponde-energization of the second relay.

19. Car-carried apparatus for automatic train control systemscomprising, an air brake system including an engineers brake valve, anequalizing reservoir, and a source of fixed pressure; a normallyenergized'brake control device adapted when de-energized to act on saidair brake system and cause an automatic brake application which cannotbe released until the car has been brought to a stop, an energizingcircuit for said device including three branches in multiple, contactsin one branch automatically opened and closed by controlling impulsesfrom the trackway in accordance with traflic conditions,speed-responsive means driven from the wheels of the car for opening asecond branch of said circuit if the running speed of the car at anytime exceeds a predetermined speed limit, and means for closing thethird branch of said circuit provided said engineers brake valve is in abrake applying position or the pressure in the equalizing reservoir hasbeen reduced a predetermined amount less than said fixed pressure.

20. Gar-carried apparatus for automatic train control systemscomprising, an air brake system including an engineers brake valve, afluid pressure operated circuit controller coupled to said air brakesystem and closed only if a brake application of a predeter minedintensity is acting, a normally energized electro-pneurnatic valveadapted when de-energized to act upon said air brake system and cause anautomatic brake application, a normally energized stick relaycontrolling said valve, means etfective only after the car has beenbrought to a stop for restoring said stick relay after de-energizationthereof, a stick circuit for said relay including two branches inmultiple, a speed-responsive device driven from the car wheels havingcontacts for closing one of said branches only so long as the car isrunning at a speed less than a predetermined speed limit, meanscontrolled from the trackway in accordance with traffic conditions foropening and closing a vshunt circuit around said contacts of the

